1. Field of the Invention
The invention relates to a peristaltic micro-pump fashioned in the column III-nitride material system as well as the broad processing technology used to fabricate suspended micro-devices in this same material system.
2. Description of the Prior Art
In designing the driving system of a biochip, three approaches have been used in the prior art. They are the on-chip mechanical micropump, the on-chip electro-kinetic micropump and the external servo system. An on-chip mechanical micropump may be prepared directly by the micro-machining technology. If this approach is adopted, a moveable part is provided inside the microchannel of the chip. The xe2x80x9celectrostatically driven diaphragm micropumpxe2x80x9d shown by Roland Zengerle et al. in their U.S. Pat. No. 5,529,465 is a typical example. In the Zengerle device, the micropump includes a pressure chamber. Reciprocal pumping power is generated by electrostatics. With the help of two passive check valve, microflows are driven with a 350 mxcexcl/min working velocity.
A simplified xe2x80x9cmicromachined peristaltic pumpxe2x80x9d was disclosed by Frank T. Hartley in U.S. Pat. No. 5,705,018. In this device, a series of block flexible conductive strips are positioned in the internal wall of a microchannel. When a voltage pulse passes along the microchannel, the flexible conductive strips are uplifted in sequence by the electrostatics so generated, such that a peristaltic movement is generated. This peristaltic movement drives the microflow along the microchannel. In the Hartley device, the working velocity is about 100 mxcexc/min.
The on-chip mechanical micropump does not provide the function such that the chip may be repeatedly used for different samples. This is because a microchannel with moveable parts is difficult to clean up residual samples or biochemical reagents after the reaction. Another problem is that the on-chip mechanical micropump, especially the peristaltic pump, involves expensive material costs. These biochips are not suited for disposable applications.
Micro-fluidic pumps fabricated in Column III-nitride materials offer several advantages over existing implementations. For one, Column III-nitride materials offer high chemical inertness and high temperature stability, making the micropumps suitable for harsh or corrosive environments. In addition, these micropumps can be readily integrated on a single chip with the broad spectrum of opto-electronic, high speed and high power devices possible in the Column III-nitride semiconductors. As described below, these micropumps employ a comparatively simple and reliable pumping mechanism. Furthermore, they are fabricated from a versatile processing technology which enables a broad range of device layouts for superior microscopic fluid control.
The invention is a versatile processing technology for the fabrication of micro-electromechanical systems in GaN. This technology, which is an extension of conventional photo-electrochemical (PEC) etching, allows for the controlled and rapid undercutting of p-GaN epilayers. The control is achieved through the use of opaque metal masks to prevent etching in designated areas, while the high lateral etch rates are achieved by biasing the sample relative to the solution. For GaN microchannel structures processed in this way, undercutting rates in excess of 30 xcexcm/min have been attained.
The invention is illustrated in the fabrication of a micropump comprising an electro-deformable membrane and a substrate disposed below the membrane and coupled thereto. A microchannel is defined between the membrane and substrate. The microchannel is formed so as to have a longitudinal axis. An electrode structure is disposed on at least one side of the membrane along side of the microchannel.
The electro-deformable membrane is bowed to form a curvature having a symmetrical axis in the direction of the longitudinal axis of the microchannel.
The micropump further comprises a drive circuit coupled to the electrode structure to apply a sequential voltage along the plurality of opposing electrodes to peristaltically deform the electro-deformable membrane in the direction of the longitudinal axis of the microchannel.
In the illustrated embodiment the electro-deformable membrane is composed of p-type GaN, but any material having the same or similar electro-deformable properties may be employed.
The micropump further comprises two opposing pillars disposed on the substrate between the substrate and the membrane generally aligned in the direction of the longitudinal axis. The two opposing pillars are composed of n-type GaN.
The electrode structure is comprised of two opposing electrode substructures extending parallel to the microchannel. The two opposing electrode substructures each comprise a plurality of discrete electrodes arranged and configured to provide pairs of opposing electrodes on each side of the microchannel. Many equivalent electrode structures to a series of opposing electrodes may be used, including propagation line electrodes in which a traveling wave potential may be placed. It may also be possible for a single electrode rail to be provided to provide the traveling wave potential with the opposing side of the membrane left to float or grounded by an opposing rail or any other conductive means.
The invention is also characterized as a method of micropumping comprising the steps of providing a bowed electro-deformable membrane disposed above a substrate and coupled thereto so that a microchannel is defined between the membrane and substrate. A traveling wave potential is propagated along the electro-deformable membrane in the direction of the longitudinal axis. As a consequence, the electro-deformable membrane is peristaltically deformed by the traveling wave potential and hence fluid is pumped in the microchannel along the longitudinal axis.
The step of providing a traveling wave potential comprises the step of applying a potential across the electro-deformable membrane traverse to the longitudinal axis and sequentially applied along the longitudinal axis. More specifically, in one embodiment the step of providing a traveling wave potential comprises sequentially applying a plurality of discrete potentials across the electro-deformable membrane traverse to the longitudinal axis.
The step of providing a bowed electro-deformable membrane comprises providing p-type GaN membrane and two opposing pillars composed of n-type GaN under the p-type GaN membrane to anchor and space the membrane apart from an underlying substrate. The illustrated method of making the bowed electro-deformable membrane comprises the step of forming the n-type GaN pillars and the p-type GaN membrane by selectively photo-electrochemical etching two adjacent n-type GaN and p-type GaN layers.
In general the step of providing a traveling wave potential is provided by an electrode structure of two opposing electrode substructures extending parallel to the microchannel. The electrode substructures may be continuous or discrete. In the illustrated embodiment the traveling wave potential is supplied by the two opposing electrode substructures comprises across a plurality of discrete electrodes which are arranged and configured to provide pairs of opposing electrodes on each side of the microchannel.
While the apparatus and method has or will be described for the sake of grammatical fluidity with functional explanations, it is to be expressly understood that the claims, unless expressly formulated under 35 USC 112, are not to be construed as necessarily limited in any way by the construction of xe2x80x9cmeansxe2x80x9d or xe2x80x9cstepsxe2x80x9d limitations, but are to be accorded the full scope of the meaning and equivalents of the definition provided by the claims under the judicial doctrine of equivalents, and in the case where the claims are expressly formulated under 35 USC 112 are to be accorded full statutory equivalents under 35 USC 112. The invention can be better visualized by turning now to the following drawings wherein like elements are referenced by like numerals.